1. Field of the Invention
This invention relates to a novel ceramic composite article and a process for producing the same.
The ceramic composite article of this invention is suitable for used as a turbocharger for automobiles, electrodes of a secondary battery, constitutive materials for gas sensors and the like.
2. DESCRIPTION OF THE PRIOR ART
In recent years, the field for application of ceramics has been enlarged, and ceramics are used in various fields. However, ceramics are rarely used alone and are used in the form of a composite in combination with other materials. The use in this form further enlarges the field for application. If ceramics can easily be made into a composite with other materials, new functions and characteristics can be brought about.
As conventional methods for joining a ceramic to another ceramic, the following methods are known.
(i) A method comprising inserting silicon carbide powder between ceramic surfaces to be joined, and then carrying out an isostatic press treatment at a temperature of 1,600.degree. to 2,200.degree. C., is disclosed in Japanese Patent Kokai (Laid-Open) No. 84185/83. In this method, the joining temperature is high, and the dimensions and shapes of materials to be joined are limited because hot isostatic press is employed.
(ii) A method comprising applying a paste prepared from powders of CuS, LaCrO.sub.3 and SiO.sub.2 by use of an organic solvent between ceramics and then subjecting the paste to reaction with heating at 1,000.degree. to 1,200.degree. C., is disclosed in Japanese Patent Kokai (Laid-Open) No. 75976/80. This method is poor in reliability, because the mixing ratio of the powder changes depending on the kind of ceramics.
(iii) A method comprising joining a silicon nitride containing ceramics by inserting a coating layer of oxide, nitride or carbide of metal between the ceramic surfaces to be joined, is disclosed in Japanese Patent Kokai (Laid-Open) Nos. 88184/83, 93402/74, 130865/80 and 79876/83. However, none of these methods yield a sufficient joint to the metallized layer to ceramics since a metal is directly bonded to the ceramics.
On the other hand, as conventional methods for joining a ceramic to a metal, there are generally known methods which comprise conducting metallizing (W, W-Mo, Mo-Mn) on a ceramic surface and then brazing the metallizing layer to the metal.
With regard to a method for forming the metallizing layer, a description is given in Japanese Patent Kokai (Laid-Open) Nos. 113683/80 and 96784/81. However, all of these joining methods comprises direct joining of a metal to a ceramic and hence do not permit sufficient joining of the metallizing layer itself to the ceramic.